Significant increases in the concentrations of greenhouse gases in the Earth’s atmosphere owing to human combustion of fossil fuels and deforestation, is having profound effects on the world’s oceans. Two of the main effects on the marine environment are increased sea surface temperatures due to climate change, and ocean acidification. Increased sea surface temperatures are caused by the global warming effect of climate change. As the world’s atmosphere warms up, our oceans slowly absorb the heat. To date, the oceans have absorbed over 80% of the heat added to the atmosphere by climate change. This has caused an increase in global average sea surface temperature of approximately 0.69oC.
Ocean acidification refers to a decrease in ocean pH (increasing acidity) over decades or more that is caused by uptake of carbon dioxide (CO2) from the atmosphere. Because human activities are releasing CO2 into the atmosphere very quickly (a major cause of climate change), the ocean is taking up CO2 faster today than it has in the past. When CO2 dissolves in seawater, it acts like a weak acid and, through a series of chemical reactions, causes an increase in the acidity of the seawater, i.e. an increase in free hydrogen ions (H+). Additionally, increased CO2 concentration in seawater also causes a reduction in carbonate ions (CO32+), which are very important building blocks of calcifying marine species, i.e. those species that deposit shells, tubes, or other skeletal structures out of calcium carbonate (CaCO3), e.g. corals. Since the industrial revolution, the pH of the world’s oceans has decreased by approximately 0.1 units, which represents a 30% increase in H+ ions and a significant decrease in the availability of CO32+ to marine species.
As humans continue to release greenhouse gases into the atmosphere, climate change and ocean acidification will continue at a speed never seen before in the Earth’s history. Predictions of future concentrations of greenhouse gases in the atmosphere made by the Intergovernmental Panel on Climate Change (IPCC), show that by the year 2100 we can expect increases in sea surface temperature of approximately + 4oC and a further decrease in pH of 0.3 – 0.5 units (i.e. a 90 – 150% increase in hydrogen ions).
Rupert Perkins, Cardiff University. Article.
